With the upmost respect Electric Andy,what you say about your sons condition and his struggles with doing his CBT which is only training ,and not a test , going through a roundabout the wrong way, kind of demonstrates my thoughts and of many others, if they do something wrong like that,would be considered a dangerous fault and an instant failure.
Whilst I understand what you say about his compunction to follow procedures, as is often the case with other drivers, they break rules ,which they know they shouldn't would that cause your son to panic and do something dangerous.
I get some people with. ASD can be high performing people and can cope very well with unusual circumstances, but conversely they have an adverse reaction and then do something risky.
Some might say that's what Insurance is for, to compensate loss for ' Accidents', which are things unforeseen, but I 'd say the opposite.
That's my view, I was hit and seriously injured many years ago, by a speeding driver on a bendy twisty country lane with a national speed limit of 60 mph, whilst the accident investigation said the car wasn't over the speed limit, common sense says it would be stupid to drive on such a narrow lane at that speed, just because the rules say you can speed down the lane at 60 ,didn't mean he had to.
I am not suggesting your son would do that, but presumably the person that hit me had no attention difficulties....there is that danger, Equally your Son might never ever do the same, but that is an unknown